1. Field of the Invention
This invention relates to a heat or thermal transfer recording method and a heat or thermal transfer recording device by use of said method which can record good images on an image-receiving medium. Particularly, the present invention relates to a heat transfer recording method by use of said method which can record good images even on an image-receiving medium with low smoothness.
Here, the present invention is preferably applicable to, for example, the word processor, electronic typewriter, copying machine, printer and facsimile machine, etc.
2. Related Background Art
Today, various recording systems have been developed as the device for outputting inputted informations, and representative of such systems is the heat transfer recording system.
This recording system comprises generally presses an ink ribbon coated with a heat transferable ink composed mainly of a wax and a recording paper against a platen by a recording head. And, under this state, said recording head is permitted to generate heat selectively to melt the heat transferable ink coated on the ink sheet, thereby effecting transfer recording onto the recording paper. Accordingly, the above heat transfer recording system has compact size and lightweight as well as excellent low noise characteristic, and therefore has been widely used as the output device for word processors, electronic typewriters, etc.
In the above heat transfer recording system, image quality differs depending on the smoothness of the recording paper, and particularly when a recording paper with low smoothness such as rough paper, etc. is used, the edge portion of the transferred image may not always be transferred sharply.
Accordingly, in ordinary recording, the pressing force by a recording head is set at about 500 gf/cm or lower, but it has been considered to increase the head pressure when recording is effected on a rough paper as mentioned above. However, if the above head pressure is made higher, there have been involved such tasks that the melted ink may expanded by the high head pressure to appear sometimes as blurring of the recorded image or the melted ink may be penetrated deep into the paper fibers of the recording paper to make sometimes recording density insufficient, etc.
For this reason, in the heat transfer recording system, it has been difficult to set the head pressure by the recording head at said 500 gf/cm or higher.
Thus, in the above heat transfer recording system image quality differs depending on the smoothness of the recording paper, and particularly when a recording paper with low smoothness such as rough paper, etc. is used, the edge portion of the transferred image may not always be transferred sharply. Accordingly, as the ribbon to cope with a rough paper, it has been considered to use an ink ribbon coated with an ink composed mainly of a material having relatively higher melt viscosity such as a resin, etc. in place of wax.
However, the above ink composed mainly of a resin, etc. has generally strong film strength and is easily elongated, and therefore defects may be formed on the recorded image, or the image edge may not be sharply cut, which results in inferior reproducibility of fine portions of images. For improving the reproducibility of fine portions of images, it is preferable to strengthen the ribbon pressing force at the recording head, and also to peel off quickly the ink ribbon from the recording paper after heating at the heat-generating element.
For that purpose, the ink ribbon must be peeled off from the recording paper at the substrate edge of the recording head, and as shown in FIG. 22, the distance d.sub.1 from the heat generating element array H to the edge of the substrate S must be made shorter. However, between the above heat-generating element array H to the edge of the substrate S, there is generally provided a common electrode E for current passage to the heat-generating element array H with a thickness of 1 to 2 .mu.m, and if the distance at this portion is made too short, the voltage effect will occur when passing current through a large number of heat-generating elements, and at the same time variance in quantity of heat generated may occur depending on the number of the heat-generating elements subjected to current passage, whereby there is a fear that the image quality becomes unstable.
On the other hand, when the head pressure is made too high, if the pressing force length l1 of the recording head RH against the platen P in the heat-generating element array direction is longer than the width l2 of the ink ribbon I as shown in FIG. 23, the recording head RH coming out from the width direction of the ink ribbon I will squeeze the recording paper RS under a high pressure, whereby there is a fear that the recording paper RS may be damaged.